This invention relates generally to fuses and is particularly related to slow acting fuses having a wide range of current ratings. More specifically, the present invention relates to an alarm indicating or non-alarm indicating fuse which, due to its improved element components and configuration, results in a fuse with higher current ratings than available in the prior art, and that can withstand significant current inrush (surge) without opening the circuit while continuing to protect the circuit at a predetermined current overload.
It is well known that fuses provide means for protecting electric and electronic circuits against damage due to current overload by opening the circuit when the electrical current passing through the fuse exceeds the fuse""s predetermined rated current carrying capacity. A variety of alarm indicating and non-alarm indicating fuses with different current rated values are presently in use. Each alarm indicating fuse comprises a fusible element, usually metallic, which melts when the power consumed by the fuse raises its element temperature above the melting point of the fusible metal element. The physical disconnect during opening of the element between the current load terminal and current source (often referred to as xe2x80x9cbatteryxe2x80x9d) terminal permits a spring loaded contact to be disconnected from the current load and reconnects this same current source to an alarm terminal, providing a local and remote alarm indication that the fuse (and the circuit) has opened. Similarly, a non-alarm indicating fuse comprises the same construction, without the spring loaded contacts. There are many examples of such prior art fuses. Prior designs of alarm type fuses have restricted the element to a single, fast acting, type of current overload device. This has also limited the maximum current rating possible due to the high energy being transferred throughxe2x80x94and associated heat developed inxe2x80x94a single element.
Single element fuses which are in common use have inherent current rating limitations. The use of a single fusible element in this fuse type with current rating of over 15 amperes often results in overheating of the fusible element which causes damage to the fuse, fuseholder and potentially the circuit itself. In some circuits, however, alarm type fuses having a surge withstand capability and current ratings in excess of 15 amperes are required. While this capacity is possible in some fuses, e.g., the well known cartridge fuses, it is common to add a second, parallel fusible element in order to provide a fuse with higher surge withstand and slower operating speed. These two fusible elements are typically made of the same material and have the same cross section. However, these are not of the same mechanical configuration, are not alarm indicating fuses and the prior art alarm indicating fuses do not permit such construction. Therefore, there is a need for this type fuse which is slower acting, which can withstand a surge of current without opening, have higher current ratings and will continue to protect the fuse, fuseholder and circuit components against over current and heat damage.
Accordingly, it is an object of this invention to provide an alarm indicating fuse with enhanced characteristics for protecting electric and electronic circuits.
It is a further object of this invention to provide an alarm indicating fuse or non-alarm indicating fuse having improved characteristics because of its higher current rating.
It is also an object of this invention to provide a non-alarm indicating fuse or alarm indicating fuse with a wider range of current ratings which is slow acting and can withstand a surge of electric current without nuisance opening, thus protecting the fuse, fuseholder and circuit against damage and deterioration while permitting the circuit to receive adequate energy to perform its designated functions.
The foregoing and other objects of the present invention will be more clearly understood from the ensuing description of the invention and the accompanying drawings.
In accordance with the present invention an alarm indicating fuse assembly is provided comprising two fusible elements disposed electrically in parallel relative to each other. It has been discovered that by using a fuse assembly having two fusible elements in parallel, rather than one fusible element as it is now the conventional practice, the alarm indicating fuse assembly can withstand significantly greater current inrush without nuisance opening, and will permit production of alarm indicating fuses having higher current ratings, as compared to a similar fuse assembly which has only one fusible element.
The novel fuse assembly of this invention comprises an insulative body portion having a top portion and lower portion. The lower body portion has a vertical edge terminating in a first electrically conductive terminal and a sloped edge having an arcuate lower portion terminating in a second electrically conductive terminal. The lower body portion has a front surface and a rear surface, a diagonal groove in one of said surfaces and a first fusible element disposed in said groove. The first fusible element has one of its ends connected to the first electrically conductive terminal and a second end connected to an alarm member (e.g., an alarm contact and spring). The alarm member has a free upper end and a lower end connected to the second electrically conductive terminal. In the improvement which defines the novel fuse assembly of this invention, a second fusible element is stretched between, and its respective ends are electrically in contact, respectively, with the first and second contact terminals.
In a second embodiment of the present invention, the fuse assembly is substantially similar in structure as the first embodiment except that the second fusible element is encased within an electrically insulative tube, such as, e.g., a ceramic tube, in order to restrict arcing and improve safety of operation of the fuse assembly.
In a third embodiment of the present invention, the fuse assembly is substantially similar in structure as the first embodiment except that the first fusible element is connected to a second contact terminal that is not spring loaded and, therefore, will not be employed as an alarm indicator.
In a fourth embodiment of the present invention, the fuse assembly is substantially similar in structure as the second embodiment except that the first fusible element is connected to a second contact terminal that is not spring loaded and, therefore, will not be employed as an alarm indicator.